this makes for a bit of a messy union type that's 'London' | string - better suggestions for handling / communicating what I'm trying to get at here?

should i just type as a proper enum with the 9 possible regions returned by https://www.planning.data.gov.uk/dataset/region? i don't think these should change often?

This is a good question. There's basically two ways of doing this that I can think of which better describe the type we intend to be used here.

The first would be something like -

type UKRegion = string extends "London" ? never : string;

This is pretty neat as TS "trick" but basically meaningless in terms of the schema.

I think a better approach would be to define a UKRegion string union type of all 9 just as you suggest, and reference the Planning Data link as the source of these 9 strings in a comment or JSDoc.

We can then end up with Exclude<UKRegion, "London"> and Extract<UKRegion, "London"> (this second one is also the same as the string literal type "London" but is maybe more meaningful?).

Hopefully they would compile correctly into JSON schema!

One thing I'm super keen to discuss further with Planning Data is them being the custodian of these data dictionaries - I think this is a very meaningful and potentially quick win which may solve #51 in a satisfying way also.

Thanks! Updated to type out an enum with the 9 values - only glitch to the original suggestion of Exclude... and Extract is that a LondonProperty currently extends a UKProperty which then means non-intersecting type error.

So I've gone with UKProperty having full UKRegion type as initial compromise here - still more precise than string!

Ah ok - I think to make this work then we'd need an abstract (Property?) base interface and then extend both UKProperty and LondonProperty from this probably.

What you have here though is a totally fair and sensible compromise though 👍

This is a good question. There's basically two ways of doing this that I can think of which better describe the type we intend to be used here.

The first would be something like -

type UKRegion = string extends "London" ? never : string;

This is pretty neat as TS "trick" but basically meaningless in terms of the schema.

I think a better approach would be to define a UKRegion string union type of all 9 just as you suggest, and reference the Planning Data link as the source of these 9 strings in a comment or JSDoc.

We can then end up with Exclude<UKRegion, "London"> and Extract<UKRegion, "London"> (this second one is also the same as the string literal type "London" but is maybe more meaningful?).

Hopefully they would compile correctly into JSON schema!

One thing I'm super keen to discuss further with Planning Data is them being the custodian of these data dictionaries - I think this is a very meaningful and potentially quick win which may solve #51 in a satisfying way also.